Role of Protein Synthesis in Regulation of Phycobiliprotein MRNA Abundance by Light Quality in Fremyella Diplosiphon

If green light-acclimated Fremyella diplosiphon cultures are transferred to red light, the transcription from the inducible phycocyanin gene set increases at least 30-fold within 60 minutes. This effect is inhibited completely by the protein synthesis inhibitors chloramphenicol and spectinomycin. Application of chloramphenicol 30 minutes after transfer of cultures to inductive red light prevents further phycocyanin mRNA accumulation within 10 minutes. If red light-acclimated cells are transferred to green light, the phycocyanin transcript level declines by about 70% within 1 hour. Most of the green light-dependent decline results from the rapid cessation of transcription from the PC gene set. Chloramphenicol slows the decline to some extent by decreasing the rate of mRNA degradation in a light-independent manner. The accumulation of phycoerythrin mRNA after transfer of red light-acclimated cells to green light is also inhibited by chloramphenicol. However, there is no red light-dependent mechanism that rapidly halts phycoerythin mRNA synthesis after transfer of cultures from green to red light. Therefore, at least three light-dependent processes are involved in regulating phycobiliproteingene expression: chloramphenicol-sensitive processes required for the activation of phycocyanin and phycoerythrin gene sets and a chloramphenicol-insensitive process which blocks phycocyanin mRNA synthesis after transfer of cells from red to green light.